In prior art methods for producing electrolytic manganese dioxide, a manganese sulfate solution is electrolyzed with titanium, lead or graphite anodes. Recently, titanium electrodes have been used more frequently as the anode for the electrolytic processes. The reaction in a conventional electrolytic process is as follows: MnSO.sub.4 +2H.sub.2 O+2e.sup.- .fwdarw.MnO.sub.2 +H.sub.2 .uparw.
Based on this reaction, when one mole of MnO.sub.2 is produced, an equivalent amount of sulfuric acid is produced at the anode and hydrogen gas is produced at the cathode. When the electrolysis is made with a titanium electrode at a high current density, the manganese consumption at the anode is high and the supply of MnSO.sub.4 is generally not sufficient. Therefore the solution at the anode surface becomes H.sub.2 SO.sub.4 rich and passivation of the titanium electrode tends to take place. Under this condition, the upper limit of the current density with the titanium electrode is believed to be 0.8 to 1.0 amp/dm.sup.2 When a higher current density is applied, a non-conductive passivation film is produced on the titanium electrode and the continuation of the electrolytic operation becomes difficult because of the sudden increase in the bath voltage. Under a high current density and high voltage condition, the electrolytic manganese dioxide not only tends to fall from the electrode (does not adhere to the electrode), but also tends to contain .dwnarw. structure material, which is a material having poor discharge performance when used in electrochemical cell systems.
To overcome this difficulty, Japan Metals and Chemical Company developed a slurry method in which manganese dioxide is suspended in the electrolyte of the electrolytic bath. This method is disclosed in Japanese Patent 57-42711. A further improvement was made for the slurry method by using carbon powders such as carbon black or acetylene black suspended in the electrolytic bath. This method is disclosed in Japanese Patent 61-47911.
It is an object of the present invention to provide an improved method for yielding a superior electrolytic manganese dioxide having better conductivity and discharge capability when used in electrochemical cell applications.